On a raspberry pi, the default "hard drive" should be the SD card, and is accessible via `/dev/mmcblk0p1`
`/dev/sda` should refer the one of the USB port.
Also `fdisk` is pretty safe. You cannot overwrite a partition without manually deleting it.

The reason why I wrote an example on how to create a swap/partition is because I feel like most people playing with a raspberry pi are Windows/OS X/Ubuntu users in the sense that they usually do not manually create partitions and probably don't know how to create a swap using the command line.   
That's what I tend to think considering the number of tutorial on how to install a raspberry pi.

I may be wrong though, and I'm not really opposed to removing these instructions.

@AtnNn -- do you really want to remove them?